Like the title says, how does a rainbow exist twice? If we could see every electromagnetic wavelength, would we see all of those “colors” in between the first and second ring? What phenomenon causes it to happen twice and always separated by what seems to be a fixed amount/distance from each other when they happen?
In: Physics
Rainbows exist because light is being reflected inside water droplets. Entering and leaving the water bends the light by different amounts depending on its wavelength, which causes the wavelengths to separate apart. But each wavelength is always at the same angle, because all the drops are the same shape (a sphere), so you consistently see each color coming at you from a different place.
The second, dimmer rainbow that makes a “double rainbow” is simply light that has been reflected twice inside the droplet, instead of once. The same principles apply, it’s just a second angle for each wavelength to come from, creating a whole second rainbow. It’s not a continuation of the same rainbow, it’s a separate one entirely. There is a fixed distance between them because the angles of both of them are fixed – primary rainbow is ~41 degrees from opposite the sun and secondary is ~52 degrees from opposite the sun.
Rainbows do extend in non-visible light too, but not forever – water is opaque to most light.
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